The invention relates generally to semiconductor integrated circuits, and more particularly, to an apparatus and method for fabricating photo sensitive material onto a surface of a semiconductor integrated circuit, such as a spherical-shaped semiconductor device.
Conventional integrated circuit devices, or "chips," are formed from a flat surface semiconductor wafer. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several processing operations are performed on the semiconductor wafer surface. One such process is applying photo resist to the wafer to print integrated circuit patterns on the wafer's surface.
Traditionally, photo resist is made of one or more polymers and solvent by an off-site manufacturer. The photo resist is provided in liquid form to the fabrication facility for coating on the wafer surface. The resist is then dispensed onto a static or slowly rotating wafer and the wafer is spun rapidly to cover the wafers surface with an even, thin coating of the resist. Once covered, the resist is dried to remove any solvents and is available for any subsequent etch processing.
Photo resist is used to produce an "image" on the wafer surface. The image is responsive to light, so that where the light strikes, the resist becomes polymerized and more difficult to remove (i.e., the resist is developed). The non-polymerized regions may then be removed with etchants, including any layers under the non-polymerized regions. As a result, mask patterns can be placed on the wafer surface and used to create underlying circuit patterns in the semiconductor substrate.
The main requirements for resist application are that the resist be pinhole-free and of uniform and reproducible thickness. Very tight layers of resist are also generally required. However, the use of thin layers of resist requires much more attention be given to the removal of particles and gelatinous masses from the resist before it is dispensed.
There are many problems associated with conventional resist applications. For example, resist quality has a short life-span because it is difficult to maintain the solvents in liquid form in a normal environment. Solvents are used to maintain the liquid form, but must be efficiently removed during processing. Also, it is difficult to coat the photo resist on the wafer with a uniform thickness. Furthermore, although resist is filtered by the manufacturer, subsequent contamination may occur and long storage times produce more gel. To resolve this, the resist is often re-filtered just before application. What is needed is a system for applying photo resist to a substrate that does not experience the quality deterioration and maintenance difficulties associated with conventional resist applications.
In a continuing effort to provide an all-dry lithographic process, both dry application and dry developing of the resist are desired. Thus far, no production-worthy success has been achieved with dry resist application, and no production-worthy plasma-developable resists currently exist. What is needed is a system that facilitates the dry application and dry developing of photo resist.
Another problem with conventional photo resist applications is that they only work with relatively flat, wafer-shaped substrates. In U.S. Pat. No. 5,955,776 filed on May 16, 1997, a method and apparatus for manufacturing an integrated circuit on a spherical-shaped semiconductor is disclosed. Inherently, the technique of applying photo resist to a portion of a spherical shaped substrate and then spinning the substrate to spread the resist does not work well. Therefore, what is needed is a system that can apply the photo resist to various shaped substrates, such as a spherical-shaped semiconductor substrate.